What jets on a stock 70 GS 350 QJet

What are the stock jets for a 70 GS 350 Qjet? I want to start with the stock jets and adjust from there but I don't think mine are the correct stock size.

Thanks
Matt

 

Larry,

Thanks.

Matt

 

Keep in mind that the factory used an adjustment screw in the baseplate and "post" on the bottom of the power piston to precisely located the "B" series rods in the jets. They also used smaller main airbleeds on those carburetors, nearly as I can remember.

The best method to tune one, is to free up the APT screw in the baseplate, if possible? They can be stubborn to get to turn, and snap off easily.

We install an external screw here. This provides full control of the A/F ratio at part throttle from rich to lean without taking the carburetor apart.

The tuner then only needs to determine the best jet size for heavy/full throttle operation, then fine tune the part throttle with the APT screw.

Swapping jets and metering rods around in those carburetors can get one in trouble quickly. I've been seeing a lot of early Buick carburetors lately, and many well meaning tuners have installed HUGE jets in them to add some fuel to light/part throttle in lieu of raising the metering rods. The large jets are more often than not, WAY too much fuel for heavy part throttle operation.....Cliff

 

Swapping jets and metering rods around in those carburetors can get one in trouble quickly. I've been seeing a lot of early Buick carburetors lately, and many well meaning tuners have installed HUGE jets in them to add some fuel to light/part throttle in lieu of raising the metering rods. The large jets are more often than not, WAY too much fuel for heavy part throttle operation.....Cliff[/QUOTE]

Cliff,

Exactly why I asked my original question. My current jets are too big as I suspected. So I wanted to know what they should be before I start playing.

Thanks
Matt

 

Measure the main airbleeds, both pairs, and post the size(s).

Base the starting point (jet size) on the size of the main airbleeds. If you can't get the APT screw in the baseplate free'd up, tuning will have to be done by changing the primary rods.

This is not easy if the APT system and stock power piston are being used, as it may locate the metering rods in the jets toward the smaller end of the upper section.

The "B" series rods used in those carburetors have a very slight taper to the upper section, so fine tuning could be done at the factory with the APT screw in the baseplate.

They will typically show up a bit lean at light-part throttle. Uneducated tuners immediately throw more jet at them, or less metering rod, or both. In most cases, the jet size was adequate right to start with, the metering rods either needed to be raised up a tad, or replaced with smaller ones.....Cliff

 

Larry, I'm pretty sure your book isn't correct. I believe the main jets should be .067 not .069. I have the 350 SP block not a 455.o No:

I changed mine to .067, tuned everything, adjusted timing about 34 total, and it's running pretty good now.

Thanks
Matt